Manufacture of tetraethyl pyrophosphate



Patented Oct. 23, 1951 MANUFACTURE OF TETRAETHYL PYROPHOSPHATE John Sterling Harris, Richmond Heights, Mo., assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. Application May 1, 1948, Serial No. 24,683

2 Claims. (Cl. 260461) This invention relates to. compositionsv containing increased amounts of tetraethyl pyrophosphate, and more. particularly to a. process for the manufacture of tetraethyl pyrophosphate.

Compositions containing tetraethyl pyrophosphate are widely used as agricultural economic poisons, particularly against many insects such as aphids and against many acarina such as the red spider mites, however, such compositions may be-used generally against the lower forms of life which, in the past,- have been combatted by the use of nicotine or. nicotine salts. Furthermore, tetraethyl pyrophosphate has been found useful in the preparation of insectivo'ricide and rodenticide compositions.

Whilethe art has.disclosedlseveralmethods for the; preparation of. tetraethyl pyrophosphate, most of these methods are. of interest only from a. purely academic and theoretical viewpoint. Prior. to thisinvention, there has not been a practicalv commercial process for the productionv of tetraethyl pyrophosphate in good yields from readily available raw materials. It has become known to the art that when phosphorus oxychloride is reacted with the neutral triethyl ester of ortho-phosphoric acid in a mol. ratio of about 1:3 at temperatures of about 130 C. to 150 C., while the resulting mixture of reaction products contains predominantly hexaethyl tetraphosphate, there is also. present in the mixtures of reaction products about l2%, and seldom more than of tetraethyl pyrophosphate. It is extremely diiiicult and tedious-to concentrate or separate the tetraethyl pyrophosphate from the mixture of'reaction products as almost allofthese reaction products are subjectto hydrolysis when in contact with water and when separation is. attempted by fractional distillation, the fractionation must be carried out under avacuum of a fraction of a millimeter of mercury, as decomposition of the tetraethyl pyrophosphate takes place at the temperatures required for'distillation under a lower vacuum and maintenance of such very highvacuums for distillation purposes. is extremely expensiveand undesirable. in acommercial process.

It is an object of'this invention, therefore, to provide a process for the production of tetraethyl pyrophosphate in substantially increased yields over the yields obtained" by the processes. presently known to the art. A further objectis to provide a process for the production of) reaction mixtures containing'tetraethyl pyrophosphate in substantially increased concentrations over the concentrations obtained" from the processes pres- 2 enty known to the art. A still further-object of this invention is to provide biological toxicant compositions containing increased amounts of tetraethyl pyrophosphate which possess over 300% greater biological activity for the combating' and control of pests such as aphids and mites than do the compositions containing tetraethyl pyrophosphate which are presently known to the art.

In the practice of this invention, the mixtures of. reaction products from the processes of this invention contain substantially 40% that is 38-45%, of tetraethyl pyrophosphate as contrasted with the processesv of the prior art which yieldedmixtures of the reaction products containing only l015% of the tetraethyl pyrophosphate. For uses where substantially pure tetraethyl pyrophosphate is required, the tetraethyl pyrophosphate may be separated from the mixtures of reaction products by high vacuum fractional distillation (below one millimeter'of mercury) or by one of the solvent extraction methods as are described and claimed in the United States application Serial No. 24,918 filed May 3, 1948, now United States Patent No. 2,523,613 of Dvornikofi or patent application Serial No. 24,672, filed May 1, 1948, now United States Patent No. 2,523,243 of Willis. It is evident that when substantially pure tetraethyl pyrophosphate is required, that the recovery of the tetraethyl pyrophosphate from the reaction mixture of this invention containing 38-45% of tetraethyl pyrophosphate is much more efficient and is to be preferred over the recovery of the tetraethyl pyrophosphate from the reaction mixtures of the prior art which contain only 10-15 of tetraethylpyrophosphate. However, the reaction mixtures themselves from the processes of this invention may be advantageously and satisfactorily used as biological toxicants, likewise these reaction mixtures as such may be used to formulate biological toxicant compositions without first separating the tetraethyl pyrophosphate from the reaction mixtures. The mixtures of reaction products from the processes of this invention are over 300% as biologically active against such pests as'aphids'and mites as are thecompositions containing only 10-15 of tetraethyl pyrophosphate which are presently known to the art;

I have discovered that tetraethyl pyrophosphate maybe obtained in substantially 40% yields by the reaction of hexaethyl tetrapolyphosphate with triethyl phosphate in the mol ratio of substantially 1v mol of the hexaethyl tetrapolyphosphate to Z'mols of'th'e triethyl phosphate. This reaction may be carried out within the temperature range of 125 C. to 160 C. However, the optimum yields are obtained when the reaction is carried out at a temperature of substantially 145 C.

While the highest yields of tetraethyl pyrophosphate are obtained when hexaethyl tetrapolyphosphate is reacted with triethyl phosphate in the mol ratio of 1 mol of hexaethyl tetrapolyphosphate to substantially 2 mols of triethyl phosphate, yields of substantially 40% tetraethyl pyrophosphate may be obtained when 1.5 to 3 mols of triethyl phosphate are reacted with 1 mol of hexaethyl tetrapolyphosphate. However, it is preferred to hold the mol ratio within the ratio of 1 mol of hexaethyl tetrapolyphosphate to 1.9 to 2.1 mols of triethyl phosphate. In carrying out the process of this invention, the hexaethyi tetrapolyphosphate need not be separated from the mixtures of reaction products by which the hexaethyl tetrapolyphosphate was made. Rather, the triethyl phosphate may be added to the reaction mixtures containing the hexaethyl tetrapolyphosphate in the proper mol proportions and the reaction carried out under the described conditions to obtain reaction mixtures containing tetraethyl pyrophosphate in a substantially 40% yield.

The following examples are illustrative of the method by which this invention may be practiced, however, it is not intended that this invention be limited solely to the processes as set forth in the following examples:

Example I 506 g. (1 mol) of hexaethyl tetraphosphate were slowly warmed to 135 C. in a glass reaction vessel equipped with a reflux condenser and 364.4 g. (2 mols) of triethyl phosphate were gradually added, with stirring, to the warmed hexaethyl tetraphosphate at such a rate so as to maintain a, reaction temperature of about 135 C. After all of the triethyl phosphate had been added to the hexaethyl tetraphosphate, the reaction mixture was then heated to about 145 C. and thereafter maintained at 145 C. for an additional two hours during which time the reaction mass was continuously stirred. Quantitative chemical analysis of the reaction mixture indicated that the reaction mixture contained 40.5% tetraethyl pyrophosphate, and biological assay of the reaction mixture indicated that the biological activity of this reaction mixture was more than 300% greater than the biological activity of compositions .containing hexaethyl tetrapolyphosphate or the compositions containing -15% tetraethyl pyrophosphate which are known to the art.

Example 11 The mixture of reaction products from Example I, containing 40.5% tetraethyl pyrophosphate was fractionally distilled under a very high vacuum (0.5 millimeter of mercury) and substantially pure tetraethyl pyrophosphate recovered.

Example III 4 slowly added, in a drop-wise manner and with stirring, to the triethyl phosphate. After all of the phosphorus oxychloride had been added to the triethyl phosphate, the temperature was maintained at 150 C. for an additional hour to finish 011 the reaction. In addition to the hexaethyl tetraphosphate present, quantitative chemical analysis of the reaction mixture indicated a 10.9% content of tetraethyl pyroph0sphate.

Example IV The reaction mixture from Example III was then heated to C. and 121.4 g. mol)- of triethyl phosphate was then added to this first reaction mixture, with stirring, and at a rate so as to maintain a reaction temperature of about 135 C. After all of the triethyl phosphate had been added, the temperature of the reaction mixture was increased to C. and this temperature was maintained and the stirring continued for an additional two hours, yielding a second reaction mixture. Quantitative chemical analysis of this second reaction mixture indicated a 41.2% content of tetraethyl pyrophosphate.

Example V A portion of the mixture of reaction products from Example III containing 41.2% tetraethyl pyrophosphate was fractionally distilled under a vacuum of 0.6 millimeter of mercury and the substantially pure tetraethyl pyrophosphate recovered.

Example VI 546.6 g. of triethyl phosphate were placed in a, glass reaction vessel equipped with reflux condenser. The triethyl phosphate was warmed to 130 C., at atmospheric pressure, and 143.4 g. of phosphorus oxychloride (a mol ratio of 311) were gradually added, with stirring, to the warmed triethyl phosphate at such a rate so as to maintain a reaction temperature of about 130 C. which required about two hours. After all of the phosphorus oxychloride had been added to the triethyl phosphate, the reaction mixture was then slowly heated to 145 C. over a period of one hour and thereafter maintained at 145 CL; for an additional hour. Quantitative chemical analysis of this reaction mixture indicated a 15.0% content of tetraethyl pyrophosphate.

Example VII Thereafter, the reaction mixture from Example VI was warmed to 130 C. and364.4 g. (2.0 mols) of triethyl phosphate were slowly added to the reaction mixture at such a rate so as to maintain a reaction temperature of about 130 C. After all of the triethyl phosphate had been added, the temperature was raised to 145 C. over a period of one hour and thereafter, while the stirring of the reaction mixture was continued, the reaction mixture was held at 145 C. for an additional two hours. Quantitative chemical analysis of the reaction mixture indicated a 41.7% content of tetraethyl pyrophosphate.

Example VIII U. S. Patent No. 2,402,703 to Woodstock also relates to the production of hexaesters of tetraphosphoric acid.

A reaction mixture containing substantially: hexaethyl tetraphosphate was prepared according to the teachings of that patent:

156 g of P295 were slowly added to and reacted 5 with 400 g. of triethyl phosphate at 5.0? (31in a cooled glassireactionvessel. TheJP2Q5liWaS$added ata"such:a1rate:so:as'ztox maintain: a; reaction teme perat'ure of about 50" C. Thereafterithe. mixture? was stirred? for: an additionalftwov hours to give a. first.- reaction. product which, according to"U..S'. Patent. No. 2,402,703, is:pr.edominantly hexaethyl tetraphosphate;

This first reaction mixture" containing" predominantly hexaethyl tetraphosphate. is: then slowlyheated, with stirring; .to 120? C...in;a'. glass reactionv vessel' and an additional400 g. of triethyl. phosphate are slowly; added; .whilei'thestinring. is continued: and: the temperature.- is' maintained': at 120 C;. Thereafter, the temperature is increasedltol 145 C. and the reaction mixture is: continuously" stirred; while: the temperature is maintainedat 145 C. forian additional two hours, yielding a second" reaction mixture containing substantially tetraethyl pyrophosphate.

Example IX A portion of the mixture of reaction products from Example V containing 41.7% tetraethyl pyrophosphate. was fractionally distilledunder a vacuum of 0.4 millimeter of mercury and substantially pure tetraethyl pyrophosphate recovered.

In the above examples, the hexaethyl tetra- 5 phosphate, or the reaction mixture containing hexaethyl tetraphosphate', may have been maintaine'dat a temperature with the range of 120 C. to 150 C. during the addition of the triethyl phosphate, however; it is' preferred to maintain I the temperature at. 120 C. to 130 C. during the addition of the triethyl phosphate. The temperature during the finishing period, that is the period following the completed addition. of

the triethyl phosphate to the hexaethyl tetraphosphate or reaction mixture containing the hexaethyl tetraphosphate, may be from 130 C. to 160 C. for a finishing period of 1 to 5 hours, the longer periods of time being required at the lower temperatures of about 130 C., and the use of the higher temperatures of 150 C. to 160 C. during the finishing period being limited by a resulting darkening of the product due to decomposition. The preferred finishing conditions are a temperature of about 142 C. and a period of 2 to 3 hours.

If it is desired, the tetraethyl pyrophosphate, which is produced in accordance with the directions of the above examples, may be separated from the reaction mixtures by fractional distillation, or otherwise, or the mixtures of reaction products containing the tetraethyl pyrophosphate may be used as such in the formulation of compositions for use as economic poisons. These mixtures of reaction products, containing substantially 40% tetraethyl pyrophosphate may be formulated into either liquid or powder types of compositions of increased biological activity. For example, one of the above mixtures of reaction products containing substantially 40% tetraethyl pyrophosphate may be formulated by spraying the said mixture onto finely ground diatomaceous earth. In the control of aphids and mites, a dust containing about 5% of tetraethyl pyrophosphate is usually satisfactory and such a dust may be prepared by spraying 97.5 pounds of finely ground diatomaceous earth with 12.5 pounds of a mixture of reaction products such as was described in Example I, and which contains substantially 40% of tetraethyl pyrophosphate. The

diatomaceous; earth which,has been sprayed with the reaction mixture containing, the. tetraethyl pyrophosphate is: then tumbled in.a rotary drum until the dust is well-mixed.

In place of. the diatomaceous earth, talcv or pyrophyllitemay be used as the inert diluent or solid. carrier for the tetraethyl pyrophosphate. Amore-readily wettable powder may be prepared by mixing 1% of a wetting agent, with the diatomaceous earth, or other carrier or-inert diluent, and subsequently spraying the mixture of carrier and; wetting agent with a reaction mixture or a solvent solution of a reaction mixture containing tetraethyl.pyrophosphate, and then tumbling the sprayedmixture in a rotary drum until the dust is well-mixed.

Insome instances, it is more desirable to have a liquid'mixture, of tetraethyl pyrophosphate and a liquid. carrier, which is suitable for spraying.

Such a liquid mixture may be prepared by dissolving about one part of a wetting agent and. one part of one of the mixtures of reaction products, such as was prepared in Example I, in 1600 parts of water. While water is the most con,-

' veniently used liquid carrier, other suitable liquid carriers. are aromatic solvents such as benzene, toluene, xylene and. naphthalenes.

Suitable. wettingagents for use in liquid mixturesorforthe preparation of the wettable dusts, as described above, may be the alkali metal salts of a.mono-,.di-ortri-sulfonate or sodiumdodecyl benzene sulfonate. Other types of sulfated and sulfonated wetting agents which are also suitable are. the sulfo-succinic acid dialkyl esters such as. sodium dioctyl sulfo-succinate and the decyl or dodecylsodium sulfates. Also suitable are the poly-ethylene oxide condensation products. of alkyl substituted phenols (wherein the alkyl substituent contains 4 to 18 carbon atoms) with 8 to 25 mols of ethylene oxide, for example the condensation product of 1 mol of octyl phenol with 10 to 12 mols of ethylene oxide.

The mixtures of reaction products containing substantially 40% tetraethyl pyrophosphate of this invention may also be formulated into concentrates for forming oil-in-water emulsions for use as insecticidal compositions. A self-dispersing, water dispersible concentrate for forming stable oil-in-water emulsions may be prepared by preparing a mixture containing 85.0% xylene, 5.0% dodecylbenzene sodium sulfonate, 5.0% of the condensation product of 1 mol of octyl phenol and 10-12 mols of ethylene oxide and 5% of the mixture of reaction products containing substantially 40% tetraethyl pyrophosphate such as was described under Example I in accordance with the practice of this invention. The above concentrate may be added to water in almost any proportion desired for the formation of a permanent oil-in-water emulsion for use as an insecticidal composition against aphids and red spider mites.

The term biological assay, often times referred to as the bioassay, of a composition is an indication of the biological activity of a particular insecticidal composition. Herein, in this description and the claims, the term insect, when used as insect or insecticide, is used in the common or popular sense to include the allied classes of Arthropods such a the Hexapoda and the Arachnida. Biological assays were run on the mixture of reaction products which were derived in accordance with the procedures described in Examples IV and VII which are representative of the present invention and on the material prepared in accordance with Examples III and VI which are representative of the material prepared in accordance with the prior art.

The biological assays were carried out in the following manner:

In each test, twenty third instar milk-weed bugs were placed on a filter paper in petri dishes and exposed in a standard laboratory spraying tower to a constant volume of atomized mist of the toxicant composition being tested. The toxicant is diluted to the desired concentration with water containing a wetting agent in the ratio of one part of the wetting agent to 1600 parts of water. After exposure, the bugs are transferred to clean dishes and counts are made after a lapse of a period of ten minutes. The tests are repeated until the minimum concentration of toxicant has been determined which will consistently produce a kill of 95% of the bugs. The minimum concentration is referred to as the LD 95 value.

When tested in accordance with the above procedure, the following LD 95 values were determined for the mixtures of reaction products which were prepared as described in Examples III, IV, VI, and VII:

Percent LD 95 Example VII 0.05 LD 95 Example IV 0.06 LD 95 Example VI 0.18 LD 95 Example III 0.26

Bearing in mind that Examples IV and VII are representative of the compositions produced in accordance with this invention, and Examples III and VI are representative of the prior art, it is readily apparent that the compositions of this invention have more than 300% greater biological activity than those compositions of the prior art.

Having described and set forth my invention in detail and having given examples showing material improvement of my process over the processes of the prior art,

I claim:

1. In a process for the manufacture of tetraethyl pyrophosphate, the step comprising reacting together at temperatures between the limits of C. and 160 C. and for a period of at least one hour substantially 2 molecular proportions of triethyl phosphate and the reaction product obtained by reacting at temperatures between the limits of 125 C. and 150 C. 1 molecular proportion of phosphorus oxychloride and substantially 3 molecular proportions of triethyl phosphate.

2. In a process for the manufacture of tetraethyl pyrophosphate, the steps comprising adding at temperatures between the limits of 125 C. and C. substantially 2 molecular proportions of triethyl phosphate to a, reaction product obtained by reacting together at temperatures between the limits of 125 C. and C. 1 molecular proportion of phosphorus oxychloride and substantially 3 molecular proportions of triethyl phosphate, and thereafter maintaining the temperature of the reaction at 140 C. to C. for 1 to 5 hours.

JOHN STERLING HARRIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,336,302 Schrader Dec. '7, 1943 2,402,703 Woodstock June 25, 1946 2,462,057 Adler Feb. 22, 1949 2,510,033 Kyrides May 20, 1950 OTHER REFERENCES Cavalier, Comptes rendus, vol. 142 (1906). pp. 885 to 887.

Hall et al., Ind. 8: Eng. Chem., Vol. 40 (April ,1948) pp. 694 to 699. 

1. IN A PROCESS FOR THE MANUFACTURE OF TETRAETHYL PYROPHOSPHATE, THE STEP COMPRISING REACTING TOGETHER AT TEMPERATURES BETWEEN THE LIMITS OF 125* C. AND 160* C. AND FOR A PERIOD OF AT LEAST ON EHOUR SUBSTANTIALLY 2 MOLECULAR PORPORTIONS OF TRIETHYL PHOSPHATE AND THE REACTION PRODUCT OBTRAINED BY REACTING AT TEMPERATURES BETWEEM THE LIMITS OF 125* C. AND 150* C. 1 MOLECULAR PROPORTION OF PHOSPHORU OXYCHLORIDE AND SUBSTANTIALLY 3 MOLECULAR PROPORTIONS OF TRIETHYL PHOSPHATE. 